Vacuum processing chambers are generally used for etching or chemical vapor depositing (CVD) of materials on substrates by supplying process gas to the vacuum chamber and applying a radio frequency (RF) field to the gas. The method of injection of process gasses into the chamber may have a dramatic effect on the distribution of chemically reactive species above the substrate surface and thus the overall process. Showerhead gas injection and diffusive transport systems are commonly used to ensure even distribution of the process gas over the substrate. In the case of inductively coupled plasma etch chambers, for example, the evolution of etched features is largely governed by the spatially dependent density of these reactive species over the substrate and the distribution of energetic ions incident on the substrate.
In spite of the developments to date, there still is a need for optimizing plasma processing of a substrate.